Spectral balancing filter for fluorescent sources

ABSTRACT

A balancing means and a method for producing spectrally balanced light is provided which comprises an optical transmission carrier and dye thereon selectively absorbing at least about 25 percent of the peak emissions of mercury discharge spectral energy sources.

United States Patent Inventor Harbans Singh Tampa, Fla. (Box 37 Rte. 1, Odessa, Fla., 33556) Appl. No 583,789

Filed Oct. 3, 1966 Patented June 28, 1971 SPECTRAL BALANCING FILTER FOR Wavelength [56] References Cited UNITED STATES PATENTS 3,227,044 1/1966 Hunt et al. 350/315 OTHER REFERENCES Clark, L. D.; Light Balancing Filters for Color Photography" PSA Journal (Section B); Vol. 198 N0. 3; August l953;pp. 112- 117.

Primary ExaminerDavid Schonberg Assistant Examiner-Robert L. Sherman Attorney-BueBlenko & Ziesenheim ABSTRACT: A balancing means and a method for producing spectrally balanced light is provided which comprises an optical transmission carrier and dye thereon selectively absorbing at least about 25 percent of the peak emissions of mercury discharge spectral energy sources.

(Milli microns) Absorbunce Absorbunce Absorbonce PATENTEDJUN28l9TI 3588215 SHEET 1 0F 5 Fig.|

Wavelength (Millimicrons) Fig.2.

Wavelength (Millimicrons) Wavelength (Millimicrons) INVENTOR Harbona Sinqh Absorbunce PATENTEnJunzelsn 3.588.215

SHEET 2 BF 5 Fig.6.

Spectral Response Wovclenq'h (Millimicrons) Fig Absorbunce m m b iv 6 Wavelonqih (Millimicrons) INVENTOR 300 350 400 soo e00 100 slnoh Wavelength (Millimicrons) g 7 /gfl zffi/fiw PATENTED Ju-28|91| 3.588.215

' SHEET 3 OF 5 Sp echo! Response Wavelength (Miliimicrons) Fl g 8.

Spectral Response Wavelength (Millimicrons) INVENTOR W) Hurbons Sinqh 6 Spectral Response Spectral Response PATENTED JUH28 l97l Fig.9.

32o aso F ig.l0.

SHEET [1F 5 Wavelength (Millimicrons) 400 440 Wavelength 480 (Millimicrons) INVENTOR Hurbons Slnqh SPECTRAL BALANCING FILTER FOR FLUORESCENT SOURCES This invention relates to spectral balancing means and methods of spectral balancing and particularly to spectral balancing means for use in order to properly balance the spectral emission of carbon arc and mercury discharge spectral energy sources.

I shall particularly describe the invention in connection with a typical mercury discharge spectral energy source, fluorescent lighting. Fluorescent lighting is very much used for illumination in offices, public buildings and homes. It has many advantages for general illumination, being soft, and very efficient. However, it is well known that fluorescent lighting is unbalanced in its spectral emission characteristics and cannot be satisfactorily used for many purposes where a balanced spectrum is required. Many attempts have been made in the past to find a satisfactory method for balancing the spectral emission of fluorescent sources or to correct the inherent difficulties by modifying the spectral distribution characteristics of fluorescent sources, but without success. I have invented a means and method of spectrally balancing fluorescent sources which may be used wherever a balanced fluorescent source is desired.

I shall particularly describe the invention in connection with photography using color film. It is well known that fluorescent lighting cannot be used satisfactorily for color photography. Consequently, when television or motion picture cameras are being used for color reproduction under artificial light, special lighting sources must be used. If the objects to be photographed are also illuminated by fluorescent artificial light sources, the special lighting sources must overpower them; if such special lighting sources are not permanently installed at the area, they must be carried there and installed and used. This is expensive and inconvenient, but is necessary because no satisfactory method for balancing the spectral emission of fluorescent sources has been found prior to the present invention.

I have discovered a means and a method of balancing the spectral emission of fluorescent sources which makes it possible to use conventional fluorescent light sources for color reproduction. I have successfully produced photographic results under fluorescent lighting which are completely free from the washed out" appearance characteristic of color reproduction by fluorescent lighting in the past and which are comparable to color reproduction by daylight illumination.

In a preferred embodiment of my invention, I provide a spectral balancing means absorbing ultraviolet radiation without distortion of violet and deep blues and with a relative strengthening of blue green and green wavelengths of light. A device of my invention preferably selectively reduces the peaks at :3,650 angstroms, 14,050 angstroms and 24,360 angstroms and substantially absorbs the 13,130 angstroms peak characteristic of all white fluorescent light sources (cool and warm whites) presently in use. The device of my invention is preferably prepared by combining known color filter materials to produce the peculiar advantages here set out. Preferably, I combine dyes on a suitable carrier to selectively reduce the emission peaks which are characteristic of all white fluorescent light sources. Preferably, dyes are combined to get an absorbance curve similar to curves hereafter described. Preferably, I use gelatin as the carrier although any other suitable optical transmission carrier may be used to carry the d es.

In the foregoing general statement of my invention, I have set out certain objects, purposes and advantages of my invention. Other objects, purposes and advantages will be apparent from the following description and the accompanying drawings in which,

FIG. 1 is a curve of absorbance characteristics of one of the dyes combined according to my invention;

FIG. 2 is a curve of absorbance characteristics of a second dye to be combined with the dye of FIG. 1 to produce a spectral balancing means according to my invention;

FIG. 3 is a curve of absorbance of spectral emission in a I preferred embodiment of my invention;

FIG. 4 is a curve of absorbance of spectral emission in a second embodiment of my invention;

FIG. 5 is a curve of absorbance of spectral emission in a third embodiment of my invention;

FIG. 6 is a spectral response curve of an orthochromatic film exposed to the spectral emission of a typical cool-white fluorescent light source without balancing its spectral emission;

FIG. 7 is a spectral response curve of an orthochromatic film exposed to the spectral emission of a typical cool-white fluorescent light source using the embodiment of my invention of FIG. 3; v

FIG. 8 is a curve as in FIG. 7 using the embodiment of my invention of FIG. 4;

FIG. 9 is a curve as in FIG. 7 using the embodiment of my invention of FIG. 5;

FIG. 10 is a spectral response'curve of an orthochromatic film exposed to the spectral emission of a typical warm-white fluorescent light source without balancing its spectral emis sion;

FIG. 11 is a curve as in FIG. 10 using the embodiment of my invention which was also used in FIG. 3;

FIG. 12 is a curve as in FIG. 10 using the embodiment of my invention which was used in FIG. 4; and

FIG. 13 is a curve as in FIG. 10 using the embodiment of my invention which was also used in FIG. 5.

Referring to the drawings, I have illustrated in FIG. 1 an absorbance curve of one preferred dye component for combining to form the balancing means of my invention and in FIG. 2 an absorbance curve of a second preferred dye component for combining with the dye of FIG. 1 to form the balancing means of my invention.

In order to illustrate the effectiveness of the spectral balancing means, I prepared three gelatin carriers with dye combinations which wound effectively balance the spectral emission of fluorescent sources. The absorbance curve values of each device were determined using a spectrophotometer and appear in Table 1 below.

TABLE I.SPECTRAL ABSORBANCE 3. 1. 45 0. 55 1. 50 3,100.. 1.35 0.40 1.50 3, 200-. 0. 0. 35 1. 30 3, 300-.- 0. 60 0. 30 0.83 a, 400. 0. 05 0. 27 0. 90 a. 500- o. 70 0. 24 0. 3, 600. 0. 70 0. 22 1. 00 a. 0. e4 0. 2a 0. 94 a. 800. 0. 55 0. 25 0.85 3. 900- 0. 56 0. 21 0. 90 4.000. 0.62 0.30 1.00 4. 100. 0. 66 0. 34 1. 05 4,200.-- 0.68 0.36 1.00 4. 300. 0. 54 0. a7 1. 02 4. 400 0. 5s 0. a5 0. 95 4, 500 0.50 0. 32 0.83 4. 600 0. 44 0. 2s 0. 72 4. 700 0. as 0. 24 0. 62 4. s00 0. 34 0. 20 0. 54 900. 0. as 0. 19 0. 4s 5, 000 0. 34 0. 19 0. 41 5. 100 0.38 0. 20 0. 49 5, 200 0. 40 0.22 0. 51 5, 300 0. 42 0. 22 0. 50 5,400... 0.42 0.20 0.50 5, 500..- 0.40 0.18 0. 48 5,600... 0.38 0.18 0.44 5. 700 0. 30 0. 10 0. a5 5.8 0.19 0.10 0.22 5. 900 o. 10 0.05 0. 12 6.000.-. 0.07 0.02 0.04 5,100-.- 0. 02 0. 01 0. 00 6, 200 0. 0o 0. 00 0. 00

*At any given wavelength, the spectral absorbance value relates the amount ol spectral energy (of that specific wavelength) enteringthespectral balanclng means to the amount of spectral energy transmitted.

The absorbance curve of Embodiment 01 is plotted in FIG. 3, that of Embodiment 02 in FIG. 4 and that of Embodiment 03 in FIG. 5. Known color balancing filters for color photograph become opaque below :4,000 A. To the contrary absorbance curves of my invention disclose transmittance of spectral energy in the near ultraviolet range To illustrate the effect of my invention on the response of photographic emulsions and materials to spectral emission from fluorescent sources I had spectrographic negatives prepared exposing photographic material to fluorescent sources through a spectral balancing means of my invention and with none at all. Orthochromatic film was used rather than panchromatic film because the described spectral balancing means exhibit little transmission difference above approximately 5,800 angstroms.

When the orthochromatic film was exposed to the fluorescent source, a step-density wedge of fine-grain silver was interposed. Each step of the wedge had an incremental density of 0.14. Thus, for example, two increments totaled 0.28, which for practical purposes represents a 2X difference in transmission or, in other tenns, a one f-stop difference in lens aperture. These density increments are directly equivalent to absorption values of 0. l 4, 0.28, etc.

After the orthochromatic film was exposed, it was developed in a high-contrast, catalytic, paraformaldehydehydroquinone developer to a gamma above 3.0 and a toe" density less than 0.30. Low-contrast continuous tone spectrographic negatives were also produced, in order to verify the results of this high-contrast procedure.

To determine the spectral response curves of the orthochromatic film, positive prints were made from the spectrographic negatives onto high gamma paper and developed to high contrast. The printing exposures were timed to print maximum possible density for all densities in the original negatives of 0.40 or less. The resulting positive prints thus show directly a contour of the photographic response from all wavelengths between 3,000 and 5,800 angstroms. From the prints data were tabulated into the following Table ll and Table "I and spectral response curves were plotted, which are FIGS. 6 through 13.

TARLE II.-SPECTRAL RESPONSE OF AN ORTHOCHRO- MATIC FILM TO THE SPECTRAL EMISSION OF A. COOL WHITE FLUORESCENT LIGHT SOURCE W thout Balancing Wavelengths Efiects Balanced Balanced Balanced in of my by Embodby Embod by Embod- Angstroms Invention imen #1 iment #2 irnent #3 3, 000 42 14 28 Base 3, I .42 l4 28 Base 3, 130 84 14 56 Base 3, 200. 42 14 28 Base 3, 300. 42 14 28 Base 3. 400. .42 14 28 Base 3, 500 42 14 .28 Base 3. 600 42 14 28 Biwe 3, 6 0 98 5 84 42 3. 700 .42 14 28 14 3. 800 42 l4 42 14 3,1100 .42 .28 .42 .14 4,000.- .46 .28 .42 .14 4, 050 1. 12 .70 84 42 4,100.. .56 .28 .42 .14 4, 200.- 42 21 .42 14 4. 300 42 14 28 14 4. 360 .84 56 70 42 4, 400 .42 14 28 14 4. 500 42 l4 42 14 4, s00 .42 2s .42 .14 56 28 .56 .28

. 42 .14 28 Base 28 .07 .20 Base The printing evposurcs for making po=itive prints w re timed to print maximum possible density for all densities in the original negatives of 0.40 or less.

"This wavelength designates an average of those wavelengths which comprise this pak", which is characteristic of the spectral emission 0! a typical fluorescent light source.

TABLE III. SPECTRAL RESPONSE OF AN ORTHOCROMAT- IC FILAI TO THE SPECTRAL EMISSION OF A WARM WHITE FLUORESCENT LIGHT SOURCF Without Balancing Wavelengths Efiects Balanced Balanced Balanced in of m by Enbo'lby Embo'lby Embod- Angstroms Invention iment #1 iment #2 iment #3 .42 14 .28 Base 42 14 28 Base 42 14 28 Base 42 14 .28 Base 56 14 .28 Base .42 14 .28 Base 42 14 35 Base 42 14 .42 Base .42 Base 28 Base The printing exposures for making positive prints were timed to print maximum possible density for all densities in the original negatives of 0.40 or less.

ThLS length designates an average of those wavelengths which comprise this pcak", which is characteristic of the spectral emission of a typical fluorescent light source.

The devices used in the foregoing tests were made of gelatin containing the following dye transfer (imbibition) dyes:

In order to compare the results of using the foregoing Embodiments Ol, 02, and O3 and the results of using the filters and combinations of filters presently known and the results of not using any of them, color motion pictures for television transmission and for conventional projection were produced under both cool white and warm white fluorescent light sources. All the films exposed without use of my invention revealed the color imbalance characteristic of color film exposed to the spectral emission of fluorescent light sources. On the other hand, the films exposed using my inventions had excellent color balance.

it will be apparent from the foregoing tables and curves that my invention has a very selective absorption characteristic for peak emissions of fluorescent light sources and at the same time changes the relative transmission of wavelengths in the band $3,000 angstroms to 16,300 angstroms. Accordingly, broadly stated, my invention has a selective absorption for peak emissions of fluorescent light sources and adjusts the relative transmission of wavelengths in the band 23,000 A. to

modif cation ofthe fluorescent source phosphors.

While I have set out certain preferred embodiments and practices of my invention in the foregoing specification, it will be understood that this invention may be otherwise broadly practiced within the scope of the following claims.

l. Balancing means for producing spectrally balanced light from fluorescent sources comprising in combination an optical transmission carrier and magenta and yellow transfer dyes in the ratios lzl to 2:5 thereon selectively absorbing at least about percent of each of the peak emissions of said sources. 

